linux-kernel - [PATCH v2 06/15] powerpc/align: Don't use __get_user

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Message-Id: <d9ecbce00178484e66ca7adec2ff210058037704.1615398265.git.christophe.leroy@csgroup.eu>
Date:   Wed, 10 Mar 2021 17:46:45 +0000 (UTC)
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>
Cc:     linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: [PATCH v2 06/15] powerpc/align: Don't use __get_user_instr() on
 kernel addresses

In the old days, when we didn't have kernel userspace access
protection and had set_fs(), it was wise to use __get_user()
and friends to read kernel memory.

Nowadays, get_user() is granting userspace access and is exclusively
for userspace access.

In alignment exception handler, use probe_kernel_read_inst()
instead of __get_user_instr() for reading instructions in kernel.

This will allow to remove the is_kernel_addr() check in
__get/put_user() in a following patch.

Signed-off-by: Christophe Leroy <christophe.leroy@...roup.eu>
---
 arch/powerpc/kernel/align.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/kernel/align.c b/arch/powerpc/kernel/align.c
index c4d7b445b459..8d4c7af262e2 100644
--- a/arch/powerpc/kernel/align.c
+++ b/arch/powerpc/kernel/align.c
@@ -310,7 +310,11 @@ int fix_alignment(struct pt_regs *regs)
 	 */
 	CHECK_FULL_REGS(regs);
 
-	if (unlikely(__get_user_instr(instr, (void __user *)regs->nip)))
+	if (is_kernel_addr(regs->nip))
+		r = probe_kernel_read_inst(&instr, (void *)regs->nip);
+	else
+		r = __get_user_instr(instr, (void __user *)regs->nip);
+	if (unlikely(r))
 		return -EFAULT;
 	if ((regs->msr & MSR_LE) != (MSR_KERNEL & MSR_LE)) {
 		/* We don't handle PPC little-endian any more... */
-- 
2.25.0